The effect of dopants (Fe, Al) on the low-temperature activity and SO₂ tolerance in solvothermally synthesized MnO_x NH₃-SCR catalysts

Fe-doped MnO_x catalyst prepared by a preferred solvothermal method displayed noticeably better low-temperature (LT) NH₃-SCR performance and water stability than an analogously prepared Al-doped MnO_x catalyst. The SCR activity of both catalysts decreased markedly when exposed to SO₂, but the resultant MnFeO_x-S catalyst retained higher LT activity than MnAlO_x-S and recovered significantly more of its original activity after thermal regeneration (400 °C). Comprehensive characterization confirmed that the deactivation of the catalysts was governed by formation of stable metal sulfates, which only decomposed to a minor extent upon thermal treatment although Al doping lowered the thermal stability of the adsorbed sulfur species. Additionally, Fe doping was found to facilitate electron transfer between Mn and Fe ions and weaken the interaction between active sites and deposited sulfates during the heating procedure, which promoted re-oxidation of Mn²⁺ to catalytically active Mn³⁺/Mn⁴⁺. Altogether, the altered redox properties resulted in improved LT SCR performance, enhanced water stability, higher SO₂ tolerance and superior regeneration of the MnFeO_x catalyst.